WO2012045599A1

WO2012045599A1 - Method for adjusting a temperature of a sensor element

Info

Publication number: WO2012045599A1
Application number: PCT/EP2011/066595
Authority: WO
Inventors: Jens Schneider; Michael Fey; Ingmar Burak; Markus Riemann; Reinhard Hamann
Original assignee: Robert Bosch Gmbh
Priority date: 2010-10-06
Filing date: 2011-09-23
Publication date: 2012-04-12
Also published as: JP2013539043A; DE102010042013A1; EP2625580B1; JP5950917B2; US9625400B2; ES2605988T3; CN103140819A; EP2625580A1; CN103140819B; US20130327124A1

Abstract

A method for adjusting a temperature of a sensor element (118), which can be heated using a heating apparatus (124) and is intended to detect at least one property of a gas in a measurement gas space (112), is proposed. The method involves at least controlling the heating apparatus (124), wherein the controlling operation comprises the following method steps: a) detecting at least one actual value of at least one controlled variable of the sensor element (118), b) determining a desired value of the at least one controlled variable, c) generating at least one manipulated variable of the heating apparatus (124) by comparing the desired value and the actual value, d) carrying out at least one monitoring step, wherein at least one parameter used to adjust the temperature is checked in the monitoring step, and wherein the at least one manipulated variable is influenced on the basis of the check.

Description

Description title

Method for adjusting a temperature of a sensor element

State of the art

From the prior art, a plurality of sensor elements for detecting at least one property of a gas in a sample gas space is known. In principle, this can be any property of the gas, for example a physical and / or chemical property of the gas. In particular, the invention will be described below with reference to sensor elements for detecting a proportion, that is, for example, a partial pressure and / or a

Percent, at least one gas component in the gas. The gas component may in particular be oxygen. However, other gas components can alternatively or additionally be detected, for example

Nitrogen oxides, hydrocarbons or other gas components. However, the invention is not limited to the detection of gas components, but it can

principle, alternatively or additionally, other properties of the gas can be detected. For the detection of gas components in particular sensor elements are used, which are based on the use of at least one solid electrolyte, ie an ion-conducting solid, for example, an oxygen-ion-conducting solid. Such solid electrolytes may for example be prepared based on zirconium dioxide, for example yttrium-stabilized zirconium dioxide and / or scandium-doped zirconium dioxide. Such sensor elements are, for example, in

Automotive sector used to gas components in the exhaust gas of a

Prove internal combustion engine with at least one engine. Examples of such sensor elements are described in Robert Bosch GmbH: Sensors in motor vehicles, edition 2007, pages 154-159. The sensor elements shown there can in principle also be operated by a method according to the present invention and / or used within the scope of a sensor device according to the invention. A lambda probe is usually based on the use of at least one

galvanic oxygen concentration cell with at least one solid electrolyte.

Alternatively or additionally, so-called pump cells can also be used.

Lambda probes may have a unicellular or else a multicellular structure, wherein reference may likewise be made by way of example to the cited prior art. As a rule, such sensor elements have at least one

Heater on. Thus, the solid electrolyte is typically at a

Activation temperature of about 350 ° C for oxygen ions conductive. The nominal temperature of conventional lambda probes is generally much higher, for example at 650 ° C - 850 ° C. In order to achieve the nominal temperature regardless of the ambient conditions, for example the temperature of the exhaust gas, the sensor element is usually actively electrically heated. For this reason, most sensor elements of the type mentioned have at least one electrical heating element, which is also generally referred to below as a heating device and which is usually controlled by at least one control unit. For example, known

A zirconia-based lambda probe incorporates an integrated platinum heater, which is typically designed to provide a greater heat reserve under normal operating conditions. This means that for the operation of the

Sensor element required heater voltage or heating power is usually much smaller than the available supply voltage or

Supply power. For example, operating temperatures of 780 ° C are already achieved with heater voltages of less than 8 V in typical sensor elements of the type mentioned above. In many cases, the sensor element is not operated with a DC voltage but with a clocked RMS voltage, which is generated by pulse width modulation of a higher DC voltage (battery voltage). Accordingly, the term heater voltage may be understood below to mean both the actual voltage applied to the heater and, alternatively, an effective voltage. The output signal of a sensor element of the abovementioned type is generally functionally strongly dependent on the temperature of the sensor element. To improve the signal accuracy, it is therefore desirable to decouple the temperature of the sensor element from changes in the exhaust gas temperature and to keep it as constant as possible. For example, a temperature control of the heater voltage of a jump probe via an operating point-dependent characteristic map with the input variables of an exhaust gas temperature and an exhaust gas mass flow is customary. An increased temperature accuracy results from a temperature control of the sensor element. As a control variable, for example, an internal resistance R, of the sensor element can be used, for example, at least one cell of the sensor element, since there is usually a clear relationship between the internal resistance and the temperature of the sensor element.

For example, in the case of commercially available jump probes, an internal resistance of 220 Ω corresponds to a sensor element temperature of 780 ° C. A corresponding

Temperature control is also used in broadband probes.

Despite the improvement in signal accuracy by existing controls, there is still a need and potential for improvement in more accurate temperature settings to further improve signal accuracy of the sensor elements. In particular, the operating temperature of the sensor element should be adjustable independently of the exhaust gas temperature in order to further increase the accuracy of the signal and thus in turn enable lower emissions and more robust diagnoses. At the same time a control with a high heating power reserve should be possible without the risk of destruction of the sensor element by overheating when heated in the

basically additional on-board voltage range exists. Furthermore, the sensor element of an exhaust gas probe should be operable at as constant a temperature as possible and at the same time protected against overheating.

Disclosure of the invention

Accordingly, in order to improve known sensor elements and methods for operating these sensor elements and to at least partially realize the abovementioned objectives, a method for setting a temperature of a sensor element which can be heated by means of a heating device for detecting at least one property of a gas in a measuring gas space and a sensor device for detecting at least one Property of a gas in a sample gas chamber

proposed. As described above, the detection of the at least one property may in particular be a determination of a proportion of a gas component in the gas. The gas component may in particular be one or more of the gas components oxygen, nitrogen, nitrogen oxides, hydrocarbons or other components. The gas may in particular be an exhaust gas, in particular an exhaust gas of an internal combustion engine, and in the sample gas chamber in particular an exhaust gas tract, for example an exhaust gas tract in one

Motor vehicle. However, other applications are possible in principle. The method is used to set a temperature of the heated by a heater sensor element. Under a setting of a temperature can be a setting to a fixed or predetermined to a variable

Temperature are understood, with temperature gradients are specified. Under a setting, as will be explained in more detail below, a control and / or a regulation of the temperature can be subsumed. The heating device may in particular comprise a resistive heating device, that is, for example, at least one heating resistor, which, for example, by applying a

Heater voltage and / or a heater current can be resistively heated. The proposed method comprises the method steps described below, which can preferably, but not necessarily, be carried out in the illustrated order. Individual or several method steps can also be carried out repeatedly in time, overlapping in time or individually or repeatedly, or be carried out over longer periods of time. The method may further include other unlisted method steps.

In a first method step, at least one actual value is at least one

Controlled variable of the sensor element detected. Under a controlled variable can thereby

Basically, any measured variable of the sensor element are understood, which is for the temperature adjustment of relevance, in particular an electrical and / or thermal measurement, which correlates directly or indirectly with the temperature, that is, a measure which a conclusion on a current temperature of the sensor element or a Area of the sensor element allows. Examples of controlled variables are explained in more detail below. Instead of the actual measured quantity, variables derived from this measured variable can also be used, for example interpolated, extrapolated, filtered, amplified, digitized or other values. In this context, an actual value of the at least one controlled variable is understood to be a current value, ie a measured value or value of the controlled variable derived from the measured value, which was detected at the present time or at a time, which is preferably not more than a few seconds, for example not more than 10 seconds

in particular not more than 5 seconds, preferably not more than 1 second or even not more than 100 milliseconds ago. In a further method step, at least one desired value of the at least one controlled variable is determined. Below a setpoint value is a value of the controlled variable understood to soft the controlled variable exactly or under specification of one or more tolerance thresholds to be set. The determination of the setpoint can

in particular be effected by this setpoint is provided by a device separate from the sensor element, for example, in which this setpoint is fixed or, as will be explained below, taking into account at least one control variable, the influence of an environment of the sensor element on the temperature characterized the sensor element is determined. Accordingly, for example, at least one can determine the setpoint

Data processing device and / or at least one electronic table and / or another type of device may be provided which determines the at least one desired value and provides for the method.

In a further method step, at least one manipulated variable of the heating device is generated by means of at least one comparison of the setpoint value and the actual value. A manipulated variable is understood to be a variable, preferably an electrical signal and / or digital information, by means of which the heating device can be controlled directly or indirectly. This manipulated variable can thus, for example, as described below, for example, a heating power, a heater voltage (current or effective heater voltages can be used), a heating current or similar sizes include, by means of which the heater can be applied directly. Alternatively or additionally, however, the at least one manipulated variable may optionally also be configured such that it must first be further processed before it serves to act on the heating device, wherein, for example, at least one actuator (for example at least one

Heizspannungsgenerator and / or at least one amplifier) can be used.

In a further method step, at least one control step is carried out. In this control step, at least one parameter used for setting the temperature by means of the proposed method is checked and the at least one manipulated variable is influenced as a function of the check. In principle, one or more of the abovementioned and / or other parameters used in the method according to the invention can be used under a parameter used to adjust the temperature. In particular, the at least one

Parameter be used in the control and / or an optional superimposed and explained in more detail below control parameters, optionally also the manipulated variable itself. Examples of used for the adjustment of the temperature Parameters are listed below. A check can, in particular, as will also be explained in more detail below, be understood to mean a query as to whether the at least one parameter satisfies at least one predetermined condition or not. For example, as will be explained below, one or more threshold conditions may be specified. An influencing of the at least one manipulated variable as a function of the checking can be understood to be a direct or indirect influencing of the manipulated variable, for example by the manipulated variable or an upstream variable acting on the manipulated variable being specifically changed. The influence can include a change,

for example, a change by means of one or more correction functions,

Correction characteristics, correction factors, by means of a deduction and / or addition of a predetermined amount, by means of a substitution by a default value, in particular 0 or a maximum or minimum value, or - depending on the result of the review of the at least one parameter - a Unchangedlassen at least one manipulated variable. Instead of a single condition, it is also possible to specify a plurality of conditions which, for example, also have different conditions

Influencing can be coupled. For example, several

Checks are performed, each review or group of reviews leads to a different influence on the at least one control variable.

After carrying out the above-mentioned method steps, the heating device can be acted upon in particular by the at least one manipulated variable and / or by at least one further manipulated variable derived from the manipulated variable, for example by interposing one or more actuators. The correction of the manipulated variable preferably follows before the heating device is charged.

It is particularly preferred if the method is carried out such that at least one control variable is still detected. In this case, a control variable is to be understood to mean any variable which influences the environment of the

Sensor element characterized on the temperature of the sensor element. In particular, the control variable may comprise at least one of the following parameters: an ambient temperature of the sensor element, in particular a gas temperature, for example an exhaust gas temperature, in the sample gas space; an operating parameter of a device containing, generating or using the gas, in particular an operating range of an internal combustion engine, preferably a Engine operating point; a parameter that characterizes, in particular quantifies, a gas stream occurring in the vicinity of the sensor element, for example a volume flow and / or mass flow of the gas, for example the exhaust gas; a parameter that characterizes and in particular quantifies a temperature occurring in the vicinity of the sensor element, in particular an exhaust gas temperature, a catalyst temperature and / or a tube wall temperature; an engine speed; an engine load condition. This at least one control variable is already recorded in current exhaust systems in motor vehicles usually, for example

Exhaust gas temperatures for the operation of catalysts are important because

Engine operating points are detected by an engine control anyway and there also exhaust gas streams (mass flows and / or flow rates), for example, at a

Exhaust gas recirculation are of importance. In this respect, for example, any parameters or combinations of such parameters that are already recorded can be used as control variables for the proposed method. However, other parameters are alternatively or additionally applicable.

As indicated above, the proposed method comprises a regulation of

Heater. Optionally, this control can be at least one control of

Heating device are superimposed. While in a scheme due to a

Comparison of the setpoint and the actual value at least one manipulated variable is generated, preferably automatically, with a feedback with a closed

In a control only a specification of a control command variable, which then in the control in a corresponding

Control variable is converted without a closed circle is used. The at least one control manipulated variable generated during the control can be superimposed, for example, additively, multiplicatively, subtractively or in some other way, the manipulated variable generated during the control. Such overlays are basically known from the prior art. For example, before the superimposition, a different amplification of the manipulated variables generated in the control and in the control can follow. However, other types of superposition are possible. The

Overlaying can take place before or after an optional actuator, for example before or after a heating voltage generator. Alternatively or additionally, different actuators can also be used for the control and for the control, for example, in each case independent heating voltage generators which in each case generate heating voltages independently of one another, which subsequently, before

Loading the at least one heater, can be superimposed. The control of the heating device can take place in particular taking into account the at least one control variable, for example one or more of the above-mentioned control variables, which characterize an influence of the environment of the sensor element on the temperature of the sensor element. In this case, the same control variables can be used for the control and the control in each case or

different control variables.

The determination of the above-described setpoint can in particular under

Taking into account the at least one control variable. This means that the control can be adapted to the at least one control variable which characterizes an influence of an environment of the sensor element on the temperature of the sensor element. Alternatively or additionally, the control can also take place taking into account the at least one control variable, for example by selecting a control command variable corresponding to the at least one control variable. For example, the temperature of the gas in the measuring gas space and / or a flow of the gas in the measuring gas space can be taken into account. If, for example, the exhaust gas temperature is high, a lower heating power is generally sufficient, for example, to set the temperature of the sensor element to the corresponding desired value.

The at least one controlled variable may in particular comprise one or more of the following control variables: at least one internal resistance of the sensor element, in particular an internal resistance of at least one electrochemical cell of the sensor element, ie a combination of at least two electrodes and at least one solid electrolyte connecting the at least two electrodes; a temperature of the sensor element, which may be detectable for example by means of a separate temperature sensor; a voltage between at least two electrodes of the

Sensor element, in particular between at least two electrodes of a Nernst cell of the sensor element; a current between at least two electrodes of the

Sensor element, in particular between at least two electrodes of a pump cell of the sensor element; for example, a stream at a fixed predetermined

Pump voltage; an electrical resistance of a conductive structure, in particular a conductive structure of the sensor element, for example an electrical

Resistance of a metal structure, for example, an electrical resistance of a supply line and / or a metallic meander. Also other controlled variables or Combinations of said and / or other controlled variables are conceivable. Particularly preferred is the use of at least one internal resistance or at least one of the internal resistance of the sensor element characterizing size as a controlled variable. For example, this internal resistance can be measured by

at least one electrochemical cell of the sensor element in the short term with a

Voltage and / or current pulse is applied and the other size, such as current or voltage is measured. This internal resistance measurement can be superimposed over time to other measurements of the sensor element for detecting the at least one property of the gas or intermittently, for example by the actual detection of the property is temporarily interrupted. For example, a cell actually used as a Nernst cell of the

Sensor element can be used in the short term for a temperature measurement.

As stated above, the manipulated variable may in particular be a manipulated variable which influences a heating power of the heating device and thus an entry of thermal energy into the sensor element. In particular, the manipulated variable may include one or more of the following manipulated variables: a voltage applied to the heater

Heater voltage; a heating power applied to the heater; a heating current applied to the heater; a parameter of a pulse width modulation of a heating power applied to the heater. Combinations of the mentioned and / or other manipulated variables are also conceivable. In this case, the aforementioned manipulated variables can be used directly or, as mentioned above, variables that can be derived from these manipulated variables or variables that generate this manipulated variable. As stated above, in the control step at least one for setting the

Temperature of used parameter checked. In particular, this at least one parameter may include one or more of the following parameters: the actual value of the controlled variable, the nominal value of the controlled variable, the manipulated variable; the control variable, which characterizes an influence of the environment of the sensor element on the temperature of the sensor element. With regard to the possible embodiments of the control variable can be made to the above description. Alternatively or additionally, further parameters and / or combinations of the mentioned and / or other parameters can be used. In the control step, the mentioned and / or other parameters can be checked as individual values, for example in the one

Single value comparison with at least one threshold takes place. Alternatively or additionally, however, temporal can also be used for individual, several or all of the mentioned parameters Characteristics of the parameters are checked, for example, by temporal variations, the history of the course of said parameters, averages of said parameters over a given period of time, filtered waveforms of said parameters or other derived from the time histories of said parameters and / or other parameters secondary parameters or functions are evaluated.

Examples are explained in more detail below.

The checking of the parameter in the control step can, as described above, be configured in various ways, which can also be combined with one another as desired. In particular, the checking of the parameter may include a query as to whether the parameter (which, as explained above, is a single value, a plurality of values, derived values, time courses or similar values) reaches, falls below or exceeds at least one fixed or dynamically predetermined threshold value and, optionally, how long this is the case. For example, at least one condition may be such that the parameter should be less than or less than a predetermined threshold. Also a condition that the

Parameter should exceed a predetermined threshold or should not fall below, can be specified. The threshold value can be fixed or variable, that is dynamic, for example, adapted to one or more external control variables and / or other external parameters. Alternatively or additionally, the check may also include a query as to whether a temporal fluctuation of the parameter over a measurement period falls short of, reaches or exceeds a predefined maximum fluctuation and, optionally, how long this is the case. Accordingly, certain conditions can also be set here with regard to the fluctuations, again alternatively or additionally, the checking step can be a check in the form of a comparison of a time profile of the parameter with at least one

Include target course. Such a comparison may be made, for example, by a comparison of curves, functions, individual values, multiple values, or the like. For example, deviations, error squares, correlation functions or similar comparisons can be used to quantify a match and / or a deviation of the course from the target profile. It is also possible to combine the aforementioned checks with one another and / or with other checks. Examples will be discussed below. Further preferred embodiments of the method relate to the type of influencing the manipulated variable in the control step. So this influence can be a particular or more of the influences described below. By way of example, the influencing may include a rejection of one or more values of the parameter and / or a consequent influencing of the manipulated variable. In particular, a rejection of strongly fluctuating temporal measured values of the parameter can take place, for example a rejection of measured values of the parameter, which lie outside a predetermined tolerance range, for example a predetermined tolerance range around a temporal mean value. Alternatively or additionally, a filtering of the actual value and a resulting

Influencing the manipulated variable done. A filtering can be done for example by means of a low-pass filter and / or by means of a bandpass filter. Again alternatively or additionally, the influencing may also include at least one averaging of the actual value and a resulting influencing of the manipulated variable. Thus, for example, an actual value can be averaged over a certain period of time, wherein, for example, a geometric mean and / or an arithmetic mean can be formed. Neither alternatively or additionally, the manipulated variable can also be replaced by a fixed or dynamically predetermined minimum value or maximum value.

For example, a fixed lower limit and / or a fixed upper limit for the at least one manipulated variable can be specified. A dynamic specification can for example be done as a deviation by a control manipulated variable when a control of the control is superimposed. For example, a tolerance range can be specified by a control manipulated variable within which the manipulated variable should lie.

Examples will be described in more detail below. Neither alternatively or additionally, the manipulated variable can also be set to a default value, for example 0 or a reduced value compared to a maximum possible value. This can also be done by switching off a loading of the heater with heating energy. Again alternatively or additionally, the manipulated variable can be reduced by a predetermined amount or a predetermined correction factor. Alternatively or additionally, the manipulated variable can also be converted into a modified manipulated variable by means of at least one correction function. This at least one correction function can in principle comprise any desired corrections, for example corrections by means of one or more correction values, correction functions, correction fields or similar corrections basically known to the person skilled in the art. Neither alternatively or additionally, the influence may also include a change in at least one control loop of the setting of the temperature, in particular a shutdown of an integral part of the control loop. Again, alternatively or additionally, the influence can also be a complete and / or partial shutdown of the scheme include, for example, by completely switching to a control of the heater, such as a controller of the type described above.

In another aspect of the present invention, a sensor device is provided for detecting at least one property of a gas in a sample gas space

proposed, in particular for determining a proportion of a gas component. The sensor device comprises at least one sensor element for detecting the property.

The sensor device further comprises at least one heating device for heating at least a part of the sensor element. For example, the at least one

Heating device wholly or partly be part of the sensor element. Alternatively or additionally, however, the at least one heating device can also be accommodated in a completely different manner in the sensor device, for example as an external component. In the first case, the heating device can be integrated, for example, in a ceramic sensor element, for example a layer structure of the ceramic sensor element, as is usually the case, for example, with planar probes. In the second case, the heating device can be designed, for example, as a rod heater, as is generally the case with finger probes, for example. For example, the sensor element may be a sensor element having at least one solid electrolyte of the type described above, in particular a ceramic solid electrolyte. The sensor element may in particular comprise one or more cells, that is to say two electrodes, which communicate with one another via the solid electrolytes

Connection stand. The sensor element can be designed unicellular or multicellular. With respect to possible embodiments of the sensor element, reference may be made, for example, to the prior art described above. In principle, all types of sensor elements can be used according to the invention, in particular ceramic sensor elements. The sensor device further comprises at least one

Driving. The drive device is set up to carry out a method according to one or more of the preceding claims. The

Control device may be configured centrally or decentralized and may be completely or partially software implemented and / or hardware implemented. The drive device can also be completely or partially implemented, for example, in a central motor control. The drive device may comprise, for example, a sensor drive device for driving and / or evaluating the sensor element or signals of the sensor element. To implement the mentioned Method, the drive device may further comprise, for example, at least one control device, in which, for example, at least one controller may be included. For superposition of an optional control, the drive device may further comprise at least one control device. The control device and the control device may together constitute a heater driving device.

The proposed method and the proposed sensor device have numerous advantages over known methods and sensor devices. In particular, a sensor element with the property of a high

Heating power reserve can be realized, which could lead to the destruction of the sensor element by overheating during heating in principle permitted vehicle electrical system voltage range. However, this sensor element and the sensor device can be operated independently of the engine operating point at a constant temperature and at the same time be set up such that the sensor element can be protected against overheating. The method can basically be applied to all actively heated and temperature-controlled or temperature-controlled exhaust gas sensors.

In order to keep the sensor element temperature as constant as possible, in particular a temperature control and a temperature control can be combined, as described above. For example, the controller can be operated by means of a characteristic diagram, for example in which, as described above, one or more control variables are detected which characterize the influence of the surroundings of the sensor element on the temperature of the sensor element. Such a control can in particular be designed as a map feedforward control, which can be superimposed on said control. Such a superposition of closed loop control provides the advantage of high accuracy closed loop control, combined with a rapid response to changes in engine operating point, for example during abrupt load changes, by the preferably operating point dependent controls. This will be high

Regulator strokes avoided, and the scheme can be used, for example, only to correct a control manipulated variable generated by the controller. The control manipulated variable is also referred to below as the precontrol value. This

Method can generally be used for improved temperature stabilization. For the temperature control, in particular a jumping probe can

In particular, an internal resistance of a Nernst cell can be measured by a short-time current pulse between the measuring and reference electrodes of the sensor element. This method is known in principle from the prior art and is there, however, in usually used for diagnostic purposes. In the context of the method proposed above, the internal resistance detected in this way can be used as the actual value of the at least one controlled variable of the sensor element or as part of an actual value of the value. The determined internal resistance can then be used for the regulation of the temperature. The disadvantage associated with conventional control methods in the case of inaccurate or erroneous detection of the controlled variable is that the optimum

Operating temperature can be exceeded or fallen below or that can even be set at excessive operating temperature even damage to the sensor element, but can be avoided by the proposed control step. For example, if a permanent or temporary increased

Contact resistance occurs in the signal circuit of the sensor element, for example in the form of Kontaktierungsproblemen, conventional temperature controls tend to adjust the high measured resistance to the smaller target resistance and thereby increase the heater voltage. As a result, the sensor element is operated too hot, and the heating element integrated in the sensor element can burn out. Thus, for example, conventional sensor elements would be heated to a temperature of> 1150 ° C, if they are operated for a long time with a heater voltage of 11 V, resulting in the burning of the heater. The greater the heating power reserve of the heating device, in particular one integrated in the sensor element

Heating device is, the greater the risk of damaging overheating of the sensor element. To avoid this overheating, the regulation of the temperature is provided in the method according to the invention, which can be optionally modified or supported by one or more control variables, which can be provided for example by an engine control system.

In the proposed method, in particular, as described above, in the superimposition of the control, a map-based feedforward control can be used, with which the proposed control can be superimposed or with which the proposed control can be combined in another way. These

Pilot control can be based, in particular, on measured or modeled control variables, which are also referred to as parameters, for example, on measured or modeled characteristics of an exhaust gas system that the

Engine operating point-dependent heating and cooling behavior of the sensor element reflect well. As a fixed sensor element temperature usually a fixed

Internal resistance of the sensor element corresponds to the higher-level control can be implemented, for example as a PID controller, the measured internal resistance R, For example, compare with a setpoint. This way a can

Control variable can be determined, which can output, for example, a Heizerspannungskorrektur or designed in another way correction of the heating power relative to the target voltage of the pilot control. Overheating of the sensor element due to faulty internal resistance control is achieved by the invention

Countermeasures at least largely avoided.

Examples of possible errors of an internal resistance control, the without

Countermeasures for overheating of the sensor element or for burning the heater can be:

Faulty internal resistance control due to detection inaccurate

Resistance readings. Inaccurate resistance measurements can occur, for example, due to tolerance in an electrical circuit in a control unit, due to discrete-time and / or non-continuous internal resistance measurement and / or by measuring the internal resistance during strongly dynamic changes of the sensor element signal.

Faulty internal resistance control due to incorrect interpretation of the internal resistance measured values. A misinterpretation of the internal resistance measured values can occur, for example, if, due to corrosion and / or aging, excessive permanent or temporary contact resistances occur, for example in a plug and / or wiring harness of the

Element signal circuit.

Faulty internal resistance control increased by temporarily

Transition resistances in the heater circuit, for example in the Heizelement- driving device, for example by a loose connection. A remedy against the possibility of error (1) can, in particular, provide detection and discarding of strongly fluctuating chronologically adjacent measured values of the actual values. The detection and / or rejection of such outliers may in particular allow the sensor element internal resistance only at more stable

Measuring situation, for example, only stable lambda, but not in unstable measurement situation, for example, lambda jumps that can lead to measurement errors to measure. Another remedy against the possibility of error (1) can be a filtering of Measurements, for example, by a low pass, a temporal average or a moving average, be.

A remedy against the possibilities of error (2) and / or (3) can in particular the limitation of the heater power, for example, the heater voltage and / or the heater current and / or a corresponding influence on a pulse width modulation, offer. This remedy may in turn be measured and / or

modeled characteristics of the exhaust system are based as a control variable. In particular, this one or more additional control variables may allow

Operating point-dependent, an upper limit and / or a corridor (i.e., defined upper and lower limits) for the manipulated variable, for example, the Heizerbeaufschlagung, in particular the heater voltage, pretend, and thus to prevent overheating of the probe safely.

Possible embodiments of the control step described above and the influencing described above can be in particular:

(a) Shutdown of a sensor element heater (heater voltage 0V) when one or more of the parameters described exceeds or falls below one or more limits. For example, the shutdown of a sensor element heating can be provided if a sensor element internal resistance reaches or falls below a critical threshold and / or the exhaust gas temperature and / or another control variable that characterizes an influence of the environment of the sensor element on the temperature of the sensor element reaches or exceeds a critical threshold ,

(b) reducing the at least one manipulated variable to a safe value,

For example, a default value when the at least one parameter reaches or exceeds a limit or, for example, when the control value and / or the control variable exceeds or falls below a threshold or reached. For example, a limitation of at least one

Actuation of the heater with heating energy, such as a

Limiting the heater voltage, be provided so that a critical value can not be exceeded. Likewise, as an alternative or in addition, it may be provided to apply heating energy to the heating device, for example the Heater voltage, reduce when the exhaust gas temperature is a critical

Reaches and / or exceeds threshold.

Absolute limitation of the manipulated variable, for example, the size controlling the heating power of the heater, to a safe value if the at least one parameter, for example the at least one control variable and / or the at least one manipulated variable, exceeds or falls below a limit value for a certain time. This can be taken into account in particular that usually a certain value of the control variable and / or the manipulated variable in the short term can be uncritical, but can be critical if this is a longer time. This has been described above, as it is also possible to evaluate temporal courses. In particular, a time after which a limitation is activated,

be advantageously selected depending on a current value of the at least one parameter, for example, the at least one control variable and / or the at least one manipulated variable. It can thereby be taken into account that a higher value of the at least one parameter can lead to overheating of the probe after a shorter time than a lower value or vice versa. A further advantageous embodiment provides that the limitation can be maintained for a certain time, even if the at least one parameter, for example the at least one control variable and / or the at least one manipulated variable, briefly falls back into the uncritical range. Thus, by a suitable implementation of the control step or the test, a delayed reaction of the sensor element temperature to changes in the at least one parameter can be taken into account. For example, it can be provided, the heater voltage or another type of

To limit the heating device with heating energy, if this exceeds a certain time a critical value. The time after which this limitation is activated, may be dependent on the current value of the heating power or the heating voltage or the parameter. The limitation can be maintained for a certain time, even if the heater voltage or the heating power falls briefly below the critical value again to take into account the delayed cooling of the sensor element after a reduction in the heater voltage.

Relative limitation of the manipulated variable generated in the control to a control manipulated variable of the optionally superimposed control, for example by a relative Limitation of a heater voltage compared to a pilot heater voltage. This can be done such that the resulting from the combination of the higher-level control and the control at least one

Manipulated variable, for example, the at least one heater voltage does not leave a corridor to a pre-tax value.

(e) switching off the control, for example, the heating control, and switching to pure control, for example, to pure feedforward control, for example, if the at least one checked parameter, for example, the at least one control variable and / or manipulated variable exceeds or falls below a threshold.

For example, a shutdown of the heating control and a

Switching to pure feedforward control be provided if the

Sensor element internal resistance is implausibly high, to prevent the heating control increases the heater voltage to impermissibly high levels.

(F) switching off an optional integral portion of the control when the at least one parameter reaches, exceeds or falls below a threshold. For example, a shutdown of an integral component can be provided if the

Sensor element internal resistance is implausibly small, for example, to prevent a possibly incorrectly learned Integralanteil leads to an increase in the heater voltage, although the sensor element already has too high a temperature.

The abovementioned embodiments (a) - (f) can also be combined with one another in pairs or in groups and / or combined with other embodiments of the invention.

The variables described above, used in the proposed method, in particular the control variable or its actual value, the at least one parameter and the at least one control variable, can be detected and / or provided in various ways. These may, for example, be actual, measured quantities, which, however, may also be subjected to a post-treatment, for example signal conditioning in the form of filtering or similar methods. Also a temporal course of these sizes can be optional

be recorded and / or used. Again alternatively or additionally, the variables mentioned, in particular the actual value and / or the at least one optional Control variable, even modeled variables, which can be determined for example by means of one or more simulation methods. In the proposed method for adjusting the temperature in this way, for example, a heater voltage, a heating power, a sensor element internal resistance, temperatures (for example, an exhaust gas temperature and / or a tube wall temperature and / or other temperatures), an engine operating point (for example, an engine speed, an amount of air or the like , the engine operating point characterizing quantities), a Abgasgmassenstrom and / or exhaust gas volume flow, a time course or similar variables. The proposed method and the proposed device can generally be used in particular in temperature-controlled exhaust gas sensors of any kind, in particular, jump probes, broadband probes or other heatable exhaust gas sensors, in particular sensor elements with the property of a high heating power reserve, leading to destruction of the sensor element

Overheating during heating in the generally permissible vehicle electrical system voltage range may result. However, the invention can also be used to maintain temperature corridors below a damage limit, for example in the case of NO _x sensors, which have maximum functional accuracy at low operating temperatures. The invention is particularly, but not exclusively, applicable in the automotive field, with no limitation with respect to the vehicle segments, the

Exhaust gas composition or the use market.

Brief description of the drawings

Further details and features of optional embodiments of the invention will become apparent from the following descriptions of preferred embodiments.

Show it:

Figure 1 shows an embodiment of a sensor device according to the invention;

Figure 2 is a schematic representation of further possible details of a

sensor device according to the invention;

FIG. 3 shows an example of an age-related internal resistance characteristic shift, which can be compensated by means of the proposed method; and Figure 4 shows an embodiment of possible limitations of a heater voltage by the proposed method.

Embodiments of the invention

1 shows a first embodiment of a schematic embodiment of a sensor device 1 10 according to the invention for detecting at least one property of a gas in a measuring gas space 112. Figure 2 shows another

Embodiment. Both embodiments are described below essentially together. The sensor devices 110 each comprise one

Drive device 1 14 and at least one connected to the drive device 114 via one or more interfaces 1 16 sensor elements 1 18. Die

Drive device 1 14, however, can also be completely or partially integrated into the sensor element 1 18 itself. The drive device 114 is formed in the illustrations in Figures 1 and 2 as a unit. However, this can also be configured decentralized and, for example, can also be completely or partially implemented in an engine control system. The drive device 114 comprises a sensor drive device 120, which is set up to receive the sensor element 118 for detecting the at least one

Property to drive and / or capture corresponding signals. Furthermore, the drive device 1 14 includes a heater drive device 122, which is set up to drive at least one heater 124 of the sensor element,

For example, to apply heat energy, for example in the form of a

Heater voltage and / or a heater current, which may be configured continuously or pulsed. While Figure 1 shows possible details of the configuration of the sensor driver 120 and the sensor element 118, in Figure 2 optional details of the heater driver 122 are shown. Both figures, which can also be combined, can be referred to below.

The sensor element 1 18 is exemplified in the illustrated embodiment as a simple jump probe with the measuring gas chamber 112 facing outer electrode 126 and arranged in a Referenzgasraum 128 reference electrode 130 which are connected to each other via a solid electrolyte 132, for example, yttria-stabilized zirconia, and a cell 134 form. However, other structures of the sensor element 118 are possible. In the exemplary embodiment illustrated in FIG. 1, the sensor drive device 120 comprises a measuring device 136 in order to detect a Nernst voltage U _N at the cell 134. Furthermore, the sensor driver 120 includes

by way of example and optionally, an internal resistance measuring device 138, which may be connected in parallel to the measuring device 136 and which, for example, a

Pumping power source and / or pump voltage source 140 and a pump connected to this, for example, in series Pumpenstrommessvornchtung 142. Furthermore, a switch 144 may be provided, so that a pump voltage pulse and / or pump current pulse can be applied to the cell 134 at short notice by means of the internal resistance measuring device 138

can be applied to determine the internal resistance of the cell 134 by a corresponding current measurement of the pump current l _p , which in turn can be a measure of the temperature of the sensor element 118 and thus, for example, directly or indirectly as an actual value (in Figure 1 and in Figure 2 with "A") of a controlled variable can be used.

For possible embodiments of the heater drive device 122, reference is made below by way of example to FIG. 2. From this it can be seen that in the illustrated embodiment, the heater driver 122 may be configured in particular in several parts and, for example, at least one control device 146 and optionally at least one control device 148 may include. Furthermore, the heater driver 122 may include at least one actuator 150. This

Actuator 150 may be configured, for example, to, in accordance with one of the control device 146 prepared control variable B and / or one of the optional

Control device 148 provided control manipulated variable C, which also as

Pilot size may be designated to provide 152 electrical energy to the heater 124 via one or more heater lines. Only one actuator 150 is shown in FIG. However, it can also be provided a plurality of actuators. For example, the control device 146 and the

Control device 148 have their own, separate actuators 150, whose

Output signals can then be combined.

The control device 146, the actuator 150, the sensor element 1 18 and the sensor drive device 120 may together form a control loop 154. The

Regulating device 146 may include a comparison device 156, in which the actual value A of the controlled variable is compared with a setpoint value D of the controlled variable in order to determine the manipulated variable B therefrom. It should be noted that the Regulating device 146 may further comprise further elements. The

Control device 148 may in particular include a control actuator 158, by means of which from a reference variable E, the control variable C is formed. The manipulated variable B and the control manipulated variable C can be superposed on each other, which can be done sequentially or in parallel. This is shown greatly simplified in FIG. For example, these signals can be added. Alternatively, as described above, different actuators 150 may also be used for the control device 146 and the control device 148. To predefine the desired value D and / or the reference variable E, the heater driver 122 may further include a controller 160 indicated in FIG. This can be acted upon with at least one control variable, which is designated in Figures 1 and 2 with F and which characterizes an influence of an environment of the sensor element 1 18 to the temperature of the sensor element 118. For possible embodiments of this control variable F, reference may be made to the above description. Here in particular temperatures of the environment of the

Sensor element 1 18, for example gas temperatures and / or

Pipe wall temperatures, and / or a flow of the gas characterizing parameters. The controller 160 may, optionally taking into account this at least one control variable, the reference variable E and thus specify the

Precontrol by means of the control device 148 influence. Alternatively or additionally, the actual value E can also be specified by the controller 160. The selection of the reference variable E and / or of the desired value D can be done, for example, by using corresponding selection algorithms, for example by characteristic fields, selection functions or the like. The controller 160 may include, for example, at least one data processing device and / or at least one memory element by means of which these selection algorithms can be implemented.

Furthermore, the heater drive device may comprise one or more control elements 162, which are indicated by way of example in FIG. These can be on

be arranged in different places and can also be fully or partially summarized with the controller 160. These control elements 162 are designed to carry out the at least one control step described above, in which at least one parameter used for setting the temperature, in the illustrated embodiment, the parameters A, B and optionally the heater power provided by the actuator 150 (for example, the heater current, Heater voltage or similar parameters) can be checked and possibly influenced. For further details, reference may be made to the above description. By means of the method described above and for example by means of one or more of the sensor devices 110 described in FIGS. 1 and 2, it is possible, for example, to counteract an effect described in FIG. Thus, in FIG. 3, internal resistances R | a Nernst cell, for example the cell 134 of the

Sensor element 1 18 shown in Figure 1, for typical sensor elements 118 as a function of the temperature T of a ceramic solid electrolyte 132 applied. In this case, the curve 164 shows a new sensor element, whereas the curve 166 shows the behavior of an aged sensor element. A desired operating point of a new one

Sensor element is indicated in Figure 2 with 168. So should the temperature of the

Ideally, for example, be set to 780 ° C sensor element, which corresponds to a new sensor element to an internal resistance of 220Ω. Will this

Internal resistance R | used as a control variable, however, the curve 166 of the aged sensor element shows that in the aged sensor element this

Internal resistance of 220Ω corresponds to a temperature of 820 ° C, so one

Deviation from 40 ° C. This deviation is sensitive to the

Sensor accuracy noticeable. To reach this temperature of 820 ° C, however, a considerably higher heating capacity is required. The example in Figure 2

Thus described regulation would thus, for example, at the output of the

Comparator 156 and / or at the output of the actuator 150, higher values than in the comparison of the new sensor element. By one or more

Control elements 162, such a deviation can be detected, and it can be taken if necessary appropriate countermeasures by correction in the control step and by influencing the manipulated variable accordingly.

By way of example, FIG. 4 shows various possibilities for superimposing a control and a regulation, with simultaneous implementation of the above

described method and taking into account an exhaust gas temperature T _G as a control variable. Plotted here on the vertical axis a size that characterizes the heating power of the heater 124 and which is here designated U _H. This may, for example, be the heater voltage, although other parameters characterizing the heating power may also be applied. First, a pilot control, for example by means of the control device 148. The characteristic curves plotted in FIG. 4 show which heating power U _H at which temperature of the gas in the measurement gas space 1 12 must be provided by the drive device 14 in order to maintain the sensor element at a constant temperature, for example 780 ° C. according to FIG. to keep. At lower exhaust gas temperatures, a correspondingly higher heat output is required than at high exhaust gas temperatures. Again, curve 170 shows a characteristic of a new sensor element, whereas curve 172 shows a characteristic of an aged sensor element. Such characteristics 170, 172 may be stored in the controller 160, for example, so that

For example, the values D and E in Figure 2 can be selected accordingly.

The influencing of the at least one manipulated variable in the at least one

Control step, for example by means of the control elements 162 in Figure 2, can be done in various ways shown in Figure 4 ways. For example, an absolute cap 174 can be made to a fixed limit value of the heating power.

Alternatively or additionally, however, it is also possible, for example, to predefine dynamic limit values, for example in the form of a lower limit value 176 and / or an upper limit value 178, which can be arranged, for example, around the characteristic curves 170, 172. For example, upon reaching these limits, 174, 176, 178 default values can be taken and / or the heating power can

be turned off and / or there may be one or more others of the above

described influencing measures are taken. The curve 180 finally shows an error case in which the heating power in the range of

Exhaust gas temperatures below about 670 ° C the absolute cap 174 far

would exceed.

Claims

claims

Method for setting a temperature of a sensor element (1 18) which can be heated by means of a heating device (124) for detecting at least one property of a gas in a measuring gas space (1 12), in particular for detecting a proportion of at least one gas component in the gas, the method comprising at least one Controlling the heater (124), wherein the scheme following

Process steps include:

a) detecting at least one actual value of at least one controlled variable of the

Sensor element (1 18),

b) determination of a desired value of the at least one controlled variable,

c) generating at least one manipulated variable of the heating device (124) by means of a comparison of the setpoint value and the actual value,

d) performing at least one control step, wherein in the control step at least one parameter used for setting the temperature is checked and wherein the at least one manipulated variable as a function of

Review is affected.

Method according to the preceding claim, wherein furthermore at least one control variable is detected, wherein the control variable characterizes an influence of an environment of the sensor element (1 18) on the temperature of the sensor element (1 18), in particular a control variable selected from: an ambient temperature of the sensor element (1 18); an operating parameter of a device including, generating or using the gas, in particular an operating range of an internal combustion engine, preferably an engine operating point; a parameter characterizing a gas flow occurring in the vicinity of the sensor element (1 18); a parameter that is one in the environment of

Characterized occurring temperature sensor element and in particular quantified, in particular an exhaust gas temperature, a catalyst temperature and / or a tube wall temperature; an engine speed; an engine load condition.

3. The method according to any one of the preceding claims, wherein the method

Furthermore, a control of the heating device (124), wherein the control of the control is at least temporarily superimposed. Method according to the two preceding claims, wherein the control of the heating device (124) taking into account the control variable.

Method according to one of the three preceding claims, wherein the determination of the desired value and preferably also the control taking into account the

Tax size takes place.

Method according to one of the preceding claims, wherein the at least one controlled variable is selected from the following group: at least one

Internal resistance of the sensor element (118), in particular an internal resistance of at least one electrochemical cell (134) of the sensor element (1 18); a temperature of the sensor element (1 18); a voltage between at least two electrodes (126, 130) of the sensor element (1 18), in particular between two electrodes (126, 130) of a Nernst cell (134) of the sensor element (1 18); a current between at least two electrodes (126, 130) of the sensor element (1 18), in particular between at least two electrodes (126, 130) of a pumping cell (134) of the sensor element (1 18); an electrical resistance of a conductive structure, in particular a conductive structure of the sensor element (118).

Method according to one of the preceding claims, wherein the manipulated variable is selected from the following group: a heating voltage applied to the heating device (124); a heater power applied to the heater (124); a heater current applied to the heater (124); a parameter of a pulse width modulation of a heating power applied to the heating device (124).

Method according to one of the preceding claims, wherein the in the

Check step checked parameter is selected from: the actual value of the controlled variable; the setpoint of the controlled variable; the manipulated variable; a control variable, the

Control size an influence of the environment of the sensor element (1 18) on the

Temperature of the sensor element (1 18) characterized.

9. The method of claim 1, wherein the checking of the parameter in the control step comprises one or more of the following checks: A query as to whether the parameter reaches, falls below or exceeds at least one fixed or dynamically predefined threshold value and, optionally, how long this is the case;

A query, whether a temporal fluctuation of the parameter over a

Measuring period, reaches or exceeds a predefined maximum fluctuation and, optionally, how long this is the case; A comparison of a time profile of the parameter with at least one desired course. 10. The method according to any one of the preceding claims, wherein influencing the manipulated variable in the control step comprises one or more of the following influences:

A rejection of one or more values of the parameter and a resulting influence on the manipulated variable, in particular a rejection of strongly fluctuating temporally adjacent measured values of the parameter;

A filtering of the actual value and a resulting influencing of the manipulated variable;

An averaging of the actual value and a resulting influencing of the manipulated variable;

- A limitation of the manipulated variable by a fixed or dynamically predetermined minimum value or maximum value;

Setting the manipulated variable to a default value;

A reduction of the manipulated variable by a predetermined amount or a correction factor;

- A conversion of the manipulated variable with at least one correction function in a modified manipulated variable;

A change of at least one control loop (154) for setting the temperature, in particular a shutdown of an integral part of the

Control loop;

- A shutdown of the scheme.

Sensor device (110) for detecting at least one property of a gas in a measurement gas space (112), in particular for determining a proportion of a gas component, wherein the sensor device (110) comprises at least one sensor element (118) for detecting the property, wherein the sensor device (1 10 ) at least one heating device (124) for heating at least a part of the Sensor element (1 18), wherein the sensor device (1 10) further comprises at least one Ansteuervornchtung (1 14), wherein the Ansteuervornchtung (1 14) is filed to perform a method according to any one of the preceding claims.